include static carrier material that forms the bioreactor bed and is circulated by medium. Adherent animal cells and suspension cells can be immobilized on the carrier material. The media flow can be led from bottom to top or reversed, while the media circulation is done internally or externally. Fixed-bed bioreactors (such as CelliGen BLU bioreactors or iCELLis bioreactors) are available as single-use systems from different suppliers and allow high-cell density productions 4. See HCD.